Conventionally wall fixings are made by drilling a hole of the appropriate size in a wall, inserting a plug of fibrous or plastics material into the hole, and driving a screw into the plug.
In order to obtain a good fixing it is essential that the hole should be of the correct diameter to accommodate the plug. Thus, it is necessary for the handyman to carry a range of masonry drills and a range of plugs of different diameters to make satisfactory fixings with different gauge screws.
Even with a comprehensive range of drills the situation occasionally arises that the masonry surrounding the drill spalls and falls away thus leaving an irregular cavity usually of considerably greater size than that originally intended and totally unsuitable for the insertion of a plug. In such situations it has been proposed, for example in UK - PS No. 470,761 to ram a moist mixture of fibers and a settable material, such as cement, into the irregular cavity. A screw may be inserted in the mixture either before or after it has set. The material may be bored axially with a sharp instrument before the screw is inserted.
This procedure has several disadvantages. Firstly, great care must be taken to ensure that the mixture of fibers and settable material is rammed into the interior of the cavity and does not simply form a shallow plug immediately adjacent the entrance to the cavity. Secondly, when spalling does occur it frequently extends to one or other side of the original hole. Once the cavity has been filled and the mixture set it is often difficult to relocate the site of the initial hole with the result that an attempt may be made to locate a screw through a surface layer of the mixture and brickwork rather than into a hole filled with mixture.